Groundwater is found in the spaces between particles of rock and soil, or in crevices and cracks in rock. Much of the earth's fresh water is found in these spaces.
Groundwater flows through the ground and groundwater-bearing formations (known as aquifers), and can enter bodies of surface water such as rivers, creeks, lakes or the ocean by flowing downhill until reaching the groundwater table (the level of soil saturated with water). At this point hydrostatic pressure forces the groundwater up through the bottom sediments, sand, gravel, rock, or cobble into the bottom of the water body.
When groundwater is contaminated by chemicals, they will flow with the groundwater and up-well into the overlying body of water. It is therefore important to be able to collect a sample of this up-welling groundwater just before it up-wells into the body of water, so that its chemical composition and potential toxicity and environmental impact can be determined. However, it can be very difficult and sometimes dangerous to obtain a sample in areas of significant water depth, or where there are multiple factors (such as water depth, fast currents and turbidity) that complicate sampling.
In emergency spill situations, for example train derailments or tanker truck accidents adjacent a body of water, leaking tanks, or leaking effluent lagoons at industrial sites, it is often necessary to quickly obtain up-welling groundwater samples to determine the groundwater quality and zone of impact, to assess cleanup measures and to estimate costs and other impacts. Therefore, a fast, effective sampling device that can penetrate the bottom sediments of the water body and extract the up-welling groundwater before it mixes with the overlying body of water is needed to obtain this information, either for emergency or long term situations.
Devices are available for obtaining welling groundwater samples, such as the Trident Probe co-developed by the U.S. Navy and Cornell University (see for example: Technical Report 1902, “Coastal Contaminant Migration Monitoring: The Trident Probe and UltraSeep System”, June 2003, SSC San Diego, San Diego, Calif. 92152-5001). This device is a multi-sensor direct-push sampling device which includes three thin stainless steel probes that can measure seepage rate, temperature and conductivity, and can capture seepage samples. The device can be deployed by hand, from a boat or with the assistance of a diver, and has an “air hammer” system that can be used to help drive the probe tips into the bottom sediments. However, deployment of the Trident Probe is generally limited to calm water and relatively soft bottom conditions, and at deployment depths up to about 30 feet.
Other direct push sampling technologies include large truck or barge-mounted devices, such as the Waterloo Profiler™ and GeoProbe™ devices, which incorporate hydraulic systems to push the probes into the soil or water bed. However, these units are usually quite large and anchoring pylons are needed for barge stabilization in high current flows. These systems are also very expensive to operate, difficult to use in deep waters, and have difficulty penetrating water beds with heavy gravel cobble bottoms.
Therefore, there continues to be a need for a sampling device that can penetrate the bottom sediments of a water body and extract up-welling groundwater in a range of water depth, current and bed conditions. Such a device may also have applications for other sampling and testing methods, such as for obtaining intact core or soil samples, or insertion of long term water quality monitoring and data logging devices, seepage meters or seismic devices.